Why is Linux not widely used?

I understand what you wanted to ask, you are asking about desktop systems and the answer is that Linux (and especially Libre Office) is still stuck somewhere in late 1990s, in philosophy and usability. The reality is that MS under Balmer (strange as it sounds) invested heavily in building a large ecosystem of developers and built a large post-sales support system, and they built their development tools and features based on what we actually needed, meaning they actually listened. All of which enabled it to retain its supremacy on desktop systems through secondary sales. We love WPF, and when we build WPF app it can only run on Windows, thus we sell Windows to our clients with our application. Users use Windows on work, MS upsells Office to their company as productivity tool, they learn Office and when they buy a home computer, its Windows/Office they choose. Hence it gets widely used.

That being said, MS under Nadella is a completely different beast, it’s all about service sales, they are now more a service delivery than a software company, and those revenues make up a huge chunk of their income. As such their only use for developer ecosystem is to up-sell their services. If your product is not about selling or paying for their services, well, su*ks to be you, you get relegated to a slower or a crawling lane and are made to suffer through innate badgering of ecstatic fanbois explaining you how stupid you are not to see the light that is new MS. For years now they are cramming Azure and this crippled UWP (omg, could it be more stupid and ugly) architecture down our throats in continual attempts to revamp their marketplace and mobile platform, while somehow thinking that we will all line up as sheeple so that they could take service fees from us. It obviously hasn’t materialized, and it probably never will. So there is a huge vacuum forming in disgruntled MS dev ecosystem, which seriously gained momentum with MS killing Silverlight overnight. A vacuum that Linux could fill up by say making Mono as fast as MS JIT and porting the WPF, for start, and say making Libre Office not look like it’s made for Windows 3.11. If only they could realize what made MS great before instead of reducing it to MS hating arguments expecting people to love what they love. People are the key, and most people are not Linux geeks. So, Windows perseveres through sheer inertia.